Bitumen vulcanizing composition

ABSTRACT

Provided is a vulcanizing agent for vulcanizing bitumen, which vulcanizing agent comprises a sulphur agent and a binder, wherein the vulcanizing agent is in the form of pellets. Further provided is a process for producing a surfacing composition, which process comprises contacting bitumen with an elastomer and the vulcanizing agent of the present invention.

The present invention concerns a composition for vulcanising bitumen.The bitumen is then useful as a surfacing composition in, for example,road surfacing. The invention provides a vulcanising composition whichwhen mixed with bitumen and an elastomer gives rise to a compositionhaving improved stability and aging properties. The invention alsorelates to methods for forming the vulcanising composition and roadsurfacing composition, and to the surfacing composition itself.

It has been known for some time to add elastomeric polymers to bitumento form a useful road surfacing composition. The elastomer provides theadvantage of allowing the composition to deform under pressure (e.g.when a vehicle is driven across it) and then to return to its originalstate. This increases the lifetime of the road surface. It has also beenknown for some time to add sulphur or sulphur containing compounds tosuch compositions to further strengthen it by introducing cross-linking.This cross-linking is termed vulcanisation. The formation of suchcompositions is generally carried out in two steps: the elastomer isadded to the bitumen and fully dispersed, and then the vulcanising agentis added and cross-linking is allowed to occur. A number of publishedpatent applications describe such processes, including WO 98/47966, WO92/11321, WO 90/02776, WO 93/18092, and WO 96/15193.

A specific process of this type is disclosed in published Europeanpatent, EP 424 420. This document discloses formation of a bitumencomposition in two steps. An elastomeric polymer (SBS) is dispersed inbitumen at a temperature of around 140-180° C. When the SBS has fullydispersed in the bitumen, vulcanising agents are added, includingsulphur, a sulphur donor and other additives. The mixture is agitatedfor from 100-150 minutes at a temperature of from 140-180° C. to formthe final composition.

In published French patent application FR 2 737 216 more recentlydeveloped an alternative one-step procedure for forming a surfacingcomposition from bitumen. This method makes use of a preliminary mixtureready for use, which preliminary mixture comprises SBS in powder formand cross-linking agents in powder form. The preliminary mixture isitself thus a powder.

There are a number of disadvantages associated with all of the abovemethods. The two-step processes are more time consuming and requireseparate storage of a larger number of different components. Moreover,the elastomer and cross-linking agent are in powder form and must beadded separately. Thus, their proportions need to be determined onforming the surfacing composition. This process is prone to errorleading to wastage and increased cost. The one-step process overcomessome of these problems, but is itself associated with further problems.The preliminary mixture is in a powder form and needs to be mixed sinceit is composed of more than one ingredient. Powders are subject tosafety problems, since they are a fire and explosion hazard. This isparticularly problematic for sulphur and sulphur-containing compounds.Moreover, powders are difficult to store and are subject to clogging andcaking which makes them difficult to process.

An aim of the present invention is to solve the problems associated withthe above prior art. It is a further aim of the present invention toprovide a vulcanising composition which is safer, easier to use andgives rise to a final surfacing composition which has improvedstability, storage and aging characteristics and allows a better controlon the amount of product used in the compositions.

Accordingly, the present invention provides a vulcanising agent forvulcanising bitumen, which vulcanising agent comprises a sulphur agentand a binder, wherein the vulcanising agent is in the form of pellets.Generally the sulphur agent is dispersed with the binder. By pellets, itis meant a product comprising particulate matter collected together toform larger agglomerates. These agglomerates are not especially limitedin shape or size, provided that they are not in a hazardous powder form,and may include an extrudate, tablet or pill formed by extrusion orcompression of the vulcanising agent.

The present invention provides a pelletised vulcanising agent whichavoids the hazards associated with powders, and can be employed in aone-step process to form a road surfacing agent with an elastomer andbitumen. By one step process is meant a process in which the elastomerand vulcanising agent can be added together to the bitumen, if desired.A two-step process requires that the elastomer and bitumen arethoroughly dispersed before the vulcanising agent is added.Surprisingly, the present vulcanising agent also improves the aging andstability of the surfacing composition in addition to the aboveadvantages.

The various aspects of the present invention will now be discussed inmore detail.

The vulcanising agent comprises a binder and a sulphur agent, theproportions of which are not especially limited, provided that thebinder is present in sufficient quantity to allow pellets to be formed.In a preferred embodiment the vulcanising agent comprises 20 wt. % ormore of the binder. More preferably the vulcanising agent comprises from20-90 wt. % of the binder and from 10-80 wt. % of the sulphur agent. Thevulcanising agent may also comprise from 0-30 wt. % of furtheradditives. Preferably the sulphur agent comprises from 10-100 wt. % ofelemental sulphur and from 0-90 wt. % of a sulphur-containing compound.The sulphur agent may thus comprise a sulphur donor, such as zincdibutyl dithiocarbamate (ZDBC) or zinc mercaptobenzothiazol (ZMBT) or asulphinamide. Preferred sulphur containing-compounds and sulphur donorsmay be found in the Rubber Handbook published by the Swedish Institutionof Rubber Technology.

The binder is not especially limited, provided that it is capable ofpelletising the sulphur agent. Preferably, however, the binder has amelting point (and/or softening point) below the melting point ofsulphur, for ease of processing. In preferred embodiments, the bindercomprises a wax, a hydrocarbon resin, a copolymer of ethylene and anacrylic ester. The more preferred binders include polyethylene (PE),glycol monostearate (GMS), ethyl vinyl alcohol (EVA) and copolymers ofethylene and acrylate esters.

A particularly preferred vulcanising agent is elemental sulphur, and aparticularly preferred binder is EVA.

The vulcanising agent preferably comprises further additives. Theseadditives are not especially limited and may be added to improve mixingand/or facilitate processing. They may also be selected to improvesurface quality, especially road quality. Such further additives maycomprise tackifiers, elastomers, bitumens, zinc oxide, and/or stearicacid.

The present invention also provides a process for production of thevulcanising agent, which process comprises:

-   -   (a) extruding a sulphur agent with a binder; or    -   (b) compressing a sulphur agent with a binder, at a temperature        below the melting temperature of the sulphur agent, so as to        form pellets of the vulcanisation agent.

The process is a standard compression or extrusion process and is wellknown in the art. Standard processing techniques and devices may beemployed. The process preferably employs a temperature of 110° C. orless, since sulphur melts at around 119° C. However, if the sulphuragent as a whole has a higher melting temperature than this, then highertemperatures may be employed.

The present invention further provides a process for producing asurfacing composition, which process comprises contacting bitumen withan elastomer and a vulcanising agent as defined above. In a preferredembodiment, the process is carried out at a temperature of 100° C. ormore. More preferably the process is carried out at a temperature of120-200° C. As already mentioned above, this is a one-step process wherethe elastomer and vulcanising agent are added substantiallysimultaneously to the bitumen.

Generally from 1-15 parts by weight of elastomer are employed with from85-99 parts by weight of bitumen. Preferably from 0.01-10 wt. %, morepreferably from 0.1-5 wt. % of vulcanising agent is employed, based uponthe total weight of bitumen and elastomer.

The elastomer is not especially limited provided that it has thequalities required for surfacing compositions. Such elastomers are wellknown in the art and are generally rubbery polymers. In a preferredembodiment, the elastomer comprises styrene butadiene styrene (SBS),hydrogenated SBS, styrene isoprene styrene (SIS), styrene ethylenebutadiene styrene (SEBS) and/or polyisobutadiene (PIB).

The surfacing composition of the present invention has improved agingand stability properties and is preferably used for producing and/orrepairing a road, pavement or track, or other surface for vehicles.

Typically such surfacing compositions are made up prior to transportingthem to the site at which they are to be used. Once made up they arestored for up to three days at temperatures of around 180° C., to keepthe bitumen from solidifying. Thus, stability at high temperatures isimportant for such compositions, and it is important that thecompositions undergo as little phase separation as possible. The presentsurfacing compositions are especially stable, as shown in the ring andball test (described below) as compared with prior art compositions.

The present invention will now be described with reference to thefollowing specific embodiments, which are by way of Example only and arenot intended to limit the invention.

EXAMPLES

In the following examples, the bitumens employed were a Venezuelanbitumen (Bitumen A) having a penetration of 87 at 25° C., and a MiddleEastern bitumen (Bitumen B) having a penetration of 74 at 25° C.Additionally five chinese bitumen have been tested. They havepenetration values at 25° C. of 75, 58, 78, 83 respectively, for SH1,SH2, SH3 and SH4. The penetration test is a standard well known test inthe industry, in which the depth of penetration of a needle into thebitumen is measured. It was measured here following the methods ofstandard test ASTM D-5-73 revised 95. All these bitumen were used forlaboratory tests.

The elastomer employed in the laboratory tests was Finaprene® 503 (SBS—a31/69 wt. % styrene/butadiene polymer). The elastomers employed in theindustrial road compositions were Finaprene® 503 (SBS—a linear 31/69 wt.% styrene/butadiene polymer), Finaprene® 401 (a radial low molecularweight 20/80 wt % styrene/butadiene polymer) and Finaprene® 411X (aradial high molecular weight 30/70 wt % styrene/butadiene polymer)

The vulcanising agent comprised either:

-   -   (a) sulphur powder,    -   (b) 70/30 wt. % of sulphur/EVA pellets prepared by extrusion; or    -   (c) 70/30 wt. % of (80/20 wt. % sulphur/ZDBC)/EVA pellets        prepared by compression.    -   (d) 30/62/3/3/2 wt % of EVA/sulphur/ZDBC/ZMBT/PIB pellets        prepared by extrusion

Example 1

This is an example of the present invention.

Bitumen A was heated to 180° C. and 3 wt. % of Finaprene® 503 was addedin pellet form, simultaneously with 0.1 wt. % vulcanisation agent © inpellet form, based on the total weight of bitumen and elastomer. After120 minutes the mixture was homogeneous. The stability to storage wasgood (there was no phase separation) and confirmed the efficacy of thevulcanisation.

Example 2

This is an example of the present invention.

Bitumen B was heated to 180° C. and 5 wt. % of Finaprene® 503 was addedin pellet form, simultaneously with 0.1 wt. % vulcanisation agent (b) inpellet form, based on the total weight of bitumen and elastomer. After120 minutes the mixture was homogeneous. The stability to storage wasgood (there was no phase separation) and confirmed the efficacy of thevulcanisation.

Example 3

This is a comparative example employing a method of FR 2 737 216.

Bitumen B was heated to 180° C. and 5 wt. % of Finaprene® 503 was addedin powder form, simultaneously with 0.1 wt. % vulcanisation agent (a) inpowder form, based on the total weight of bitumen and elastomer. After120 minutes the mixture was homogeneous. The stability to storage wasless good than for Examples 1 and 2.

Stability and Aging Test Using the Ring and Ball Method.

The products of Example 2 and Comparative Example 3 were tested forstability. An internal standard method developed from the ring and ballmethod (ASTM-D36) was employed. The surfacing composition is coated on aring after it has been made, then the ring is submerged in hot oil. Thetemperature at which the composition falls away from the ring isrecorded. The composition is stored at high temperature for 3 days andthe method is repeated. If the stability is good, the composition willretain its tackiness and the temperature will ideally remain as close tothe originally measured temperature as possible. The larger the drop intemperature, the lower the stability of the composition and the worseits aging characteristics.

The results for the compositions formed in Examples 2 and 3 are shownbelow in Table 1.

TABLE 1 Drop in temp/° C. Mixing time/mins Example 2 Example 3 120 7 10180 5 10

Table 1 shows that for mixing times of 2 and 3 hours, there is a lesserdrop in temperature for the composition of the present inventioncompared with the closest prior art composition. This highlights theimprovement in aging and stability characteristics of the presentcompositions.

Examples 4 to 7

In these examples, several surfacing compositions were prepared from theChinese Bitumens SH1, SH2, SH3 and SH4, with various elastomers indifferent amounts and optionally with various amounts of heavy furfurolextract. The compositions according to the present invention wereprepared with 0.1 wt % of vulcanising agent d) in pellet form and thecomparative examples were prepared without vulcanising agent. Thecompositions and results are displayed in Tables 2 to 5. In theseexamples, the ductility was measured following the method of standardtest IP 32/55, the kinematic viscosity of asphalt was measured followingthe method of standard test ASTM D 2170 and the elastic recovery wasmeasured following the method of standard test DIN V 52021-1.

TABLE 2 Bitumen SH1. Composition wt % wt % wt % Bitumen SH1 96.5 96.495.5 Finaprene ® 503 — — — Finaprene ® 401 3.5 3.5 4.5 Vulcanising agent— 0.1 — Heavy furfurol extract — — — Properties Ring and balltemperature-° C. 68 70 80 Penetration  5° C.-{fraction (1/10)} mm 10 1113  15° C.-{fraction (1/10)} mm 18 20 18  25° C.-{fraction (1/10)} mm 5155 54 Viscosity 135° C.-Pa · s 1.22 1.47 1.54 150° C.-Pa · s 0.72 0.840.89 Ductility  5° C.-cm 13 14 20  13° C.-cm 60 80 60  25° C.-cm 62 8758 Elastic recovery-% 92 95 97 Storage stability (48 hrs at no yes no163° C.)

TABLE 3 Bitumen SH2. Composition wt % wt % wt % wt % wt % Bitumen SH297.5 97.4 96.5 96.4 95.5 Finaprene ® 503 — — — — — Finaprene ® 401 2.52.5 3.5 3.5 4.5 Vulcanising agent — 0.1 — 0.1 — Heavy furfurol extract —— — — — Properties Ring and ball temperature −° C. 53 55 67 69 74Penetration 5° C.-1/10 mm 9 10 9 10 9 15° C.-1/10 mm 16 10 15 17 16 25°C.-1/10 mm 47 44 43 51 44 Viscosity 135° C.-Pa · s 1.16 1.16 1.31 1.521.76 150° C.-Pa · s 0.63 0.70 0.79 0.85 0.98 Ductility 5° C.-cm 6 1 8 814 13° C.-cm 24 41 52 58 60 25° C.-cm 97 >130 54 82 53 Elasticrecovery-% 35 58 93 93 98 Storage stability (48 hrs at no yes no yes No163° C.)

TABLE 4 Bitumen SH3. Composition Wt % wt % wt % wt % wt % wt % wt % wt %wt % wt % wt % wt % Bitumen SH3 96.5 96.4 95.5 97.5 97.4 97.5 97.5 96.596.4 96.5 96.5 95.5 Finaprene ® 503 3.5 3.5 4.5 — — — — — — — — —Finaprene ® 401 — — — 2.5 2.5 2.5 2.5 3.5 3.5 3.5 3.5 4.5 Vulcanisingagent — 0.1 — — 0.1 — — — 0.1 — — — Heavy furfurol extract — — — — — 5%10% — — 5% 10% — Properties Ring and ball temperature-° C. 52 54 93 5052 48 45 70 72 65 58 76 Penetration 5° C.-1/10 mm 13 12 11 11 10 — — 1012 — — 10 15° C.-1/10 mm 22 23 22 21 20 — — 21 21 — — 21 25° C.-1/10 mm57 60 53 66 60 88 124 58 57 74 110 53 Viscosity 135° C.-Pa · s 1.03 1.121.28 0.89 0.99 0.86 0.67 1.18 1.30 0.95 0.79 1.51 150° C.-Pa · s 0.630.66 0.79 0.55 0.59 — — 0.67 0.78 — — 0.82 Ductility 5° C.-cm 20 32 3911 11 22 57 22 19 46 77 26 13° C.-cm 71 73 102 37 54 — — 49 74 — — 6625° C.-cm >140 >140 103 110 >130 — — 52 65 — — 52 Elastic recovery-% 6868 98 28 60 65 58 98 95 95 95 100 Storage stability (48 hrs at no yes noyes Yes yes yes no yes yes yes no 163° C.)

TABLE 5 Bitumen SH4. Composition wt % wt % wt % wt % wt % wt % BitumenSH4 97 96.9 96.5 96.4 96 95.9 Finaprene ® 503 — — — — — — Finaprene ®401 3 3 3.5 3.5 4 4 Vulcanising agent — 0.1 — 0.1 — 0.1 Properties Ringand ball Tempera- 57 59 73 74 80 82 ture-° C. Penetration 5° C.-1/10 mm10 12 14 11 11 11 15° C.-1/10 mm 23 20 22 23 19 19 25° C.-1/10 mm 68 5743 6 58 55 Viscosity 135° C.-Pa · s 1.00 1.16 1.09 1.10 1.2 1.47 150°C.-Pa · s 0.61 0.65 0.72 0.77 0.74 0.86 Ductility 5° C.-cm 15 21 16 4125 27 13° C.-cm 46 51 70 96 72 84 25° C.-cm 54 109 55 7 56 70 Elasticrecovery-% 78 73 95 98 98 98 Storage stability (48 hrs at yes yes no yesno Yes 163° C.)

The results displayed in Tables 2 to 5 clearly show that all the bitumencompositions prepared according to the present inventions had excellentstorage stability. In addition, as desired, the ring and balltemperature was higher for the compositions of the present invention.The viscosity was also higher for the compositions using the vulcanisingagent of the invention resulting in a better cohesion and so was theductility. It must be observed in Table 4 that a higher ductility can beobtained by the addition of 5 to 10 wt % of heavy furfurol extract, butat the expense of the ring and ball temperature that is lower and at theexpense of the penetration value that is higher.

Industrial Examples

Two road compositions have been prepared with the Chinese bitumen SH2,the elastomer Finaprene® 503 and the vulcanising composition d) inpellet form and in powder form respectively. The small drop intemperature observed for the laboratory tests of Examples 1 and 2 wasconfirmed for the industrial examples. This can be seen in Table 6showing the drop in ring and ball temperature as a function of ageingfor the same vulcanising agent in pellet form and in powder form.

TABLE 6 Difference in Ring and Ball Temperature after ageing.Vulcanising agent ΔT ° C. Pellets Powder 1 day at 180° C. 2.3 5.6 2 daysat 180° C. 3.3 6.0 3 days at 180° C. 3.3 5.7

1. A process for producing a surfacing composition comprising contactingbitumen with an elastomer and a pelletized vulcanizing agent comprisingpellets incorporating a particulate sulfur agent and a binder for saidsulfur agent which holds the particles of the sulfur agent together toform pellets which are larger than the sulfur agent particles withoutthe incorporation of a binder.
 2. A process according to claim 1 whereinsaid bitumen is contacted with said elastomer and said vulcanizing agentat a temperature of at least 100° C.
 3. The process of claim 2 whereinsaid bitumen and elastomer and vulcanizing agent are contacted at atemperature within the range of 120-200° C.
 4. The process of claim 2,wherein said elastomer and said bitumen are contacted in relativeamounts of 1-15 parts by weight of said elastomer and 85-99 parts byweight by said bitumen.
 5. The process of claim 4 wherein said elastomerand said bitumen are contacted in relative amounts of 1-10 parts byweight of said elastomer and 90-99 parts by weight of said bitumen. 6.The process of claim 4 wherein said vulcanizing agent is added in anamount within the range of 0.01-10 wt. % of the total weight of saidbitumen and said elastomer.
 7. The process of claim 6 wherein saidvulcanizing agent is added in an amount within the range of 0.1-5 wt. %of the total weight of said bitumen and said elastomer.
 8. The processof claim 1 wherein the elastomer is selected from the group consistingof styrene butadiene styrene, hydrogenated styrene butadiene styrene,styrene isoprene styrene, styrene ethylene butadiene styrene,polyisobutadiene and mixtures thereof.
 9. The process of claim 1 whereinsaid surfacing composition is incorporated into a road pavement.
 10. Theprocess of claim 1 wherein said elastomer and said pelletizedvulcanizing agent are added together to said bitumen.
 11. The process ofclaim 1 wherein said pellets incorporate said particulate sulfur agentin an amount within the range of 10-80 wt. % and said binder in anamount within the range of 20-90 wt. %.
 12. The process of claim 11wherein said sulfur agent comprises elemental sulfur in an amount withinthe range of 10-100 wt. %.
 13. The process of claim 12 wherein saidsulfur agent comprises a sulfur-containing compound in an amount of upto 90 wt. % of said pelletized vulcanizing agent.
 14. The process ofclaim 13 wherein said sulfur-containing compound in said pelletizedvulcanizing agent comprises a sulfur donor.
 15. The process of claim 14wherein said sulfur-containing compound in said pelletized vulcanizingagent is selected from the group consisting of zincdibutyldithiocarbamate and zinc mercaptobenzothiazol.
 16. The process ofclaim 14 wherein the binder in said pelletized vulcanizing agent isselected from the group consisting of a wax, a hydrocarbon resin, aco-polymer of ethylene and an acrylic acid, polyethylene, glycolmonostearate, and ethyl vinyl alcohol, and mixtures thereof.